Engineering the Diaphragm to Minimize Gas Crossover in Alkaline Water Electrolysis

Hydrogen, a versatile energy carrier, is essential for the transition to renewable energy systems. Electrolytically produced hydrogen using renewable sources is a core technology for decarbonizing industries and societies. However, at the end of 2021, electrolysis contributed only about 4% of global hydrogen production [1]. Various electrolytic hydrogen production techniques exist, including Proton Exchange Membrane Electrolysis (PEMEC), Solid Oxide Electrolysis (SOEC), Anion Exchange Membrane Electrolysis (AEMEC), and liquid Alkaline Water Electrolysis (AEL) [2]. AEL is the most mature and scalable technology, and it doesn't require precious metals. However, for efficiencies comparable to other techniques, AEL typically operates at low current densities of 0.2-0.5 A/cm 2 (100% of rated current density). A porous diaphragm separates the produced hydrogen and oxygen in AEL. A key limitation to part-load operation of electrolyzers is hydrogen crossover into the oxygen stream, posing a safety hazard at concentrations exceeding 4%. Diffusion of dissolved gases through the diaphragm is the main crossover mechanism in balanced AEL systems and depends on electrolyte concentration and supersaturation [3]. Therefore, addressing supersaturation can significantly enhance AEL operational flexibility [4]. While crossover is marginally affected by current density, the 2% hydrogen-in-oxygen safety limit necessitates AEL shutdown at roughly 25% of rated current density to prevent hazardous mixtures. Stiesdal Hydrogen is a climate change company developing next-generation Alkaline Water Electrolysis systems. Our hydrogen electrolyzers operate within a pressure tank, eliminating the need for a hydrogen compressor and enabling direct production at up to 35 bar. To achieve operational flexibility below 25% of rated current density without sacrificing efficiency, we have engineered a novel diaphragm with a pore structure optimized to mitigate gas crossover. [1] IRENA Hydrogen Overview https://www.irena.org/Energy-Transition/Technology/Hydrogen downloaded on 17/04 2024 08:00 MET [2] J. Hnát et al 2020 New Perspectives on Hydrogen Production, Separation, and Utilization 91-117 [3] P. Trinke et al 2018 J. Electrochem. Soc. 165 F502 [4] M. T. de Groot et al 2022 Int. J. Hydrogen Energy 47 82